Cryogenic refrigerator



Jan. 5, 1965 w. HAUMANN ETAL 3,163,994

CRYOGENIC REFRIGERATOR 5 Sheets-Sheet 1 Filed Julie 5, 1961 Tm 4. ATTUE/VfVS Jan. 5, 1965 w. HAUMANN ETAL 3,163,994

CRYOGENIC REFRIGERATOR 3 Sheets-Sheet 3 Filed June 5, 1961 United States Patent 3,163,994 CRYGGENEC REFRlGERATGR Wiifried Haumann, Indianapolis, Moses Mendez, West Lafayette, John .i. Mikoliczeax, indianapolis, and George E. Heaviiin, Danviile, l nd., assignors to Union Carbide Corporation, a corporation of New York Filed June 5, 1961, Ser. No. 114,838 13 Claims. (Cl. 62-213) This invention relates to cryogenic storage containers and particularly to cryogenic refrigerators employing a low-boiling liquefied gas to prese've perishable substances stored within the refrigerators in storage receptacles.

A most serious problem in storing perishable substances such as viable biological substances has been the difficulty of fully utilizing the storage space Within a cryogenic refrigerator. It is fairly common practice to store such perishable substances in receptacles such that individual specimens may be separately stored within the same cryogenic refrigerator. In the case of bovine semen storage, it is not unusual to find several hundred receptacles within one cryogenic refrigerator and, in such cases, the availability of utilizable storage space is obviously critical.

One attempt to solve the utilizable space problem was the employment of apparatus commonly known as a lazy susan type rotating tray. In this type of apparatus, rotating trays were horizontally positioned within the cryogenic refrigerator and were rotated by turning a vertical centrally-mounted drive shaft. Access to the trays was gained through an offset opening in the top of the cryogenic refrigerator but, inthe typical prior art lazy susan type apparatus, it was difficult to position any particular receptacle, stored on one of the trays beneath the offset opening, because the fog created by condensing air at such opening made visual identification very difficult and, consequently, was wasteful of t e liquefied gas refrigerant. Also, the lazy susan type apparatus employed by the prior art was fixed in place thereby necessitating extensive and expensive repair should a failure occur in the operability thereof inasmuch as the cryogenic refrigerator would have to be completely dismantled in order to gain access to the apparatus. Furthermore, due to their fixed position, the number of trays and consequently the space between the trays could not be varied, thereby requiring that limitations be placed on the size and shape of the receptacles that could be employed.

It is an object of this invention to provide a cryogenic refrigerator for the storage of perishable substance-containing receptacles having increased accessibility to the storage space than hitherto found in the art. It is a further object to provide improved means for storing and indexing such receptacles within a cryogenic refrigerator. Another object of this invention is toprovide such means whereby receptacles of varying configurations may be stored. Still another object is to provide storing and indexing means within a cryogenic refrigerator which are accessible from the exterior of the cryogenic refrigerator and which are readily removable therefrom for purposes of repair or alteration to suit the requirements of varyingsiZed receptacles.

These and other objects and advantages of the invention will become apparent from the following description and the accompanying drawings in which:

FIGURE 1 is a vertical view taken in cross-section of an exemplary cryogenic refrigerator illustrating the prin-.

ing the storing and indexing means in enlarged detail.

FIGURE 3 is an isometric View, certain parts being ice cut away, of a cryogenic refrigerator similar to FIG- URE 1.

FlGURE 4 is a schematic diagram of a novel electrical circuit suitable for regulating the refrigerant liquid level within the cryogenic refrigerators of FIGURES 1-3.

In general this invention comprises an improvedv thermally insulated cryogenic refrigerator for storing perishable substance-containing receptacles. Means for storing and indexing such receptacles comprising rotatable trays connected to a segmented, vertically-aligned, rotatably-mounted drive shaft within the cryogenic refrigerator are provided. Such means are readily accessible from the exterior of the cryogenic refrigerator and are easily modified to accommodate receptacles of varying configurations. Drive shaft engaging means communicating with the drive shaft and the exterior of the cryogenic refrigerator are provided for engaging a drive shaft segment actuating means such that by turning the drive shaft engaging means, selected individual trays connected to their respective drive shaft segments may be rotated.

The preferred form of the cryogenic refrigerator, as depicted in FIGURE 1, comprises an inner storage vessel it) having an annular opening at the upper end thereof, an outer shell 12 also having an annular opening at its upper end, sealing means 14 for joining the upper end of outer shell 12 to the upper end of inner vessel 10 thereby vacuum-tightly sealing an insulation space 16 between, and formed by, outer shell 12 and inner vessel it and removable cover means 18 for substantially closing the opening of the cryogenic refrigerator formed by sealing means 14. The opening formed by sealing means 14 preferably is circular and is substantially equal in diameter to the diameter of inner vessel 10. Insulation space 16 and removablecover means 13 are preferably substantially filled with opacified insulating material. The term opacified insulation as used herein refers to a two component insulating system comprising a low heat conductive radiation permeable material and a radiant heat impervious material which is capable of reducing the passage of infrared rays without significantly increasing the thermal conductivity of the insulating system.

Insulation space 16 and removable cover means 18 are preferably substantially filled with opacified insulating material taking the form of a low heat conductive material and a multiplicity of spaced radiation impervious barriers. As more fully described and claimed in copending US. application Serial No. 597,947, filed July 16, 1956, now Patent No. 3,007,596, in the name of L. C. Matsch, the low heat conductive material may be fibrous insulation which may be produced in sheet form. Examples of such a material include a filamentary glass material such as glass wool and fiber glass, preferably hving fiber diameters less than about 50 microns. Also such fibrous materials preferably have a fiber orientation substantially perpendicular to the direction of heat flow across the insulation space. The spaced radiation-impervious barriers may comprise either a metal, metal oxide, or metal coated material, such as aluminum coated plastic film or other radiation reflective or radiation adsorptive material or a suitable combination thereof. Radiation reflective material comprising thin metal foils are preferably suited in the practice of the present invention. For example, reflective sheets of aluminum foil having a thickness between 0.2 mm. and 0.002 mm. may be employed when fiber sheets are used as the low-conductive material, they may additionally serve as a support means for the relatively fragile radiation-impervious sheets. For example,

it is preferred that an aluminum foil-fiber sheet insulation be spirally wrapped around inner vessel it) with one end of the insulation wrapping in contact with inner vessel 10 and the other end nearest outer shell 12 or in actual contact therewith.

It will beappreciated that other forms of opacified insulation may be used. For example, the radiation impervious barriers may be incorporated directly into the low heat conductive material as described and claimed in ,U.S. Patent No. 2,967,152 issued in the name of L. C. Matsch et al. Such opacified powder-vacuum type might comprise, for example, equal parts by weight of copper flakes and finely-divided silica. The latter material has a very low solid conductivity value but is quite transparent to radiation. The copper flakes serve to markedly reduce the radiant heat inleak,

Even though the previously described preferred opacified insulation is more effective than straight vacuum insulation at higher internal pressure (poorer vacuum), its effective thermal insulation life is extended if the pressure can be maintained at or below a desired level such as, for example, below abobut 30 microns of mercury absolute. A gas removing material such as an adsorbent may be used in insulation space 16 to remove by adsorption any gas entering through the joints of the cryogenic refrigerator. In particular, crystalline zeolitic molecular sieves having pores of at least about 5 Angstrom units in size, as disclosed in US. Patent No. 2,900,800 issued in the name of P. E. Loveday, may be employed as the adsorbent in accordance with the teachings therein since this material has extremely high adsorptive capacity at the temperature and pressure conditions existing in insulation space 16 and is chemically inert toward any gases which might leak into such insulating space The adsorbent material may be provided within insulation space 16, for example, by blister 20 attached to the bottom of inner vessel or intermixed with the insulation material. If a blister is provided, a glass cloth 26a may be employed to provide gas communication between insulation space 16 and the adsorbent material within blister 2%.

It is also preferred that the interior of cover means 18 be evacuated to a positive pressure of less than 30 microns of mercury absolute. In addition, blister 22 containing adsorbent material and providing gas communication between such interior and the absorbent material through screen 22a is preferably located therein.

The storing and indexing means comprises a hollow, segmented, vertically-aligned, rotatably-mounted central drive shaft 24 wherein each of such segments are rotatable independently of the others and at least one such segment has a rotatable receptacle-holding tray connected thereto. As shown in the drawings, there are six such drive shaft segments, A through F, each having attached thereto respective circular trays 1 through 6. Should a greater distance between two such trays, for example, be required, a segment of drive shaft 24 having no tray connected thereto could be substituted for a segment having such a tray. The number of such segments is not critical and depends on such factors as the number of receptacles to be stored and their sizes.

Another element of which the storing and indexing means is comprised is a drive shaft segment actuating means 26. Drive shaft segment actuating means 2s is preferably located within hollow drive shaft '24 and, as shown in the drawings, includes six segment actuating elements a. through f. The number of such segment actuating elements corresponds to the number of drive shaft segments. Each se ment actuating element is independently connected to the respective drive shaft segment such that the segments are rotatable independently of one another.

. A third element of the storing and indexing means is a rotatable drive shaft engaging means 28. Drive shaft engaging means 28 is preferably vertically aligned within hollow drive shaft 24 and engages drive shaft segment actuating means 26 within hollow drive shaft 24 such that, by turning drive shaft engaging means 28, at least one of the drive shaft segments may be rotated independently of the others. Drive shaft engaging'rneans 28 extends through removable cover means 13 to the exterior of the cryogenic refrigerator such that the trays connected to the drive shaft segments may be rotated by turning drive shaft engaging means 2% from the exterior of the cryogenic refrigerator.

In the preferred embodiment of the cryogenic refrigerator, as shown in FIG. 1, inner vessel is suspended at the upper end within outer shell 12 by cylindrical sealing means 14- which is preferably a stainless steel ring. Horizontal movement of inner vessel 10 with respect to outer shell 12 is prevented by a tubular trunnion support mem ber 30 which is connected to inner vessel it} and outer shell 12 by support rings 32 and 34 respectively. Trunnion support member 39 is preferably constructed of a low heat conductive material such as thermosetting phenolic resins or epoxys. Alternately, the horizontal load may be completely received by neck tube 42.

Removable cover means 18 preferably comprises a top plate 36, a bottom plate 38, both of which are preferably constructed of stainless steel and joined at their periphery by a cylindrical shell 40 which also is preferably constructed of stainless steel. Neck tube 42 which provides access into the cryogenic refrigerator for drive shaft engaging means 23 when removable cover means 18 is in place, is centrally positioned within removable cover means 1% and attached to upper plate 36 and bottom plate 38 by, for example, upper and lower support disks 44 and 46, respectively, through upper and lower neck tube collars 4t": and 5%, respectively. Amess to a particular receptacle within the storage space within the cryogenic refrigerator is provided by an offset opening through removable cover means 1%. Such offset opening is described in detail in a subsequent paragraph.

Hollow drive shaft 2-4 comprises independently rotatable and vertically aligned segments consisting of tubes (six of which are shown, AP) which preferably are positioned one atop the other. Vertical alignment between the segments is maintained by segment alignment tubes 244F246, each of which is attached to the interior lower end of the preceeding next above segment by means such as welding. Separating each segment are hollow ring bushings Zed-242' which are preferably constructed :of a material such as Teflon. Segment F is journalled to the bottom of inner vessel 16 through bearing 52 and its housing 52a, such segment being seated in bearing 52 through extension 54 and shaft support disk 56. Aperture 58 serves as an outlet for any liquid refrigerant that might be trapped within housing 52a if hollow drive shaft 24 is positioned within inner vessel 10 while such refrigerant is in inner vessel 10. Pin 60 prevents bearing 52 from becoming misaligned. Segment A is also journalled at the top through bearing 62 seated in extension 64 of drive shaft 24. Removable cover means d8 seats in bearing 62 through coupling as, collar 68 and lower support disk 46, thereby providing vertical alignment for hollow drive shaft 24. Thus, by removing cover means 18, the internal mechanism of the storing and indexing means can be exposed and removed, if such is desired.

Drive shaft segment actuating means 26 comprises independent vertically aligned key-collars, referred to previously as segment actuating elements (six of which are shown a;f), which are centrally positioned within, and at the upper end of, hollow drive shaft 24. Each such key-c0llar is attached to its respective segment through a collar disk (Zea-26f) and a segment disk (Mar-26f) which are joined together by a drive tube (Zia-27f). Drive tubes 27a27f are concentric with one another and of respective decreasing diameter and increasing length so that each segment A-F may be joined to its respective key-collar. Brass bushings ZSa-ZSe are preferably placed between the drive tubes to provide proper alignment therebetween. It has been found that this construction of drive shaft actuating means 205 provides an efiicient drive shaft segment actuating system, however, other methods may be employed to join such key-collars to the respective drive shaft collars and the disclosure of this invention is not limited to any particular manner of such joinder.

The preferred details of drive shaft engaging means 28 and its intersection with drive shaft actuating means 26 will be described in reference to FIGURE 2.

Referring to the figure, drive shaft engaging means 28 comprises a tubular section 70, a slotted or grooved section 72, tubular section 74, solid section 76 having a sleeve 78 which contains keyway 80 and solid portion 82 having a keyway 84. The tubular sections have been used to reduce the heat leak to the container through drive shaft engaging means 28 as much as possible. Sleeve 78 moves up and down in accordance with the vertical movement of drive shaft engaging means 28 and is maintained in proper vertical position with respect to the shaft by spacers 86 and 88. Rotation of sleeve 78 with respect to the cryogenic refrigerator is prevented by the engagement of its keyway 80 with key M), being preferably welded to collar 66.

Keyway 84 of the solid portion 82 of drive shaft engaging means 28 engages the keys 92a-92f of key-collars a-f as drive shaft engaging means 28 is moved up and down. The keys 92a-92f are preferably welded to keycollars a-f which in turn are preferably welded to the particular drive structures (previously described with reference to FIGURE 1) of the segments A-F. The keys and keyways are preferably tapered to aid in the insertion and removal of drive shaft engaging means 28. As shown in the drawing, drive shaft engaging means .28 is positioned so as to drive segment A. Since keyway 84 engages each successive lower segment, the lower segments A through F will also be rotated. As drive shaft engaging means 28 is lowered, keyway 84 becomes disengaged from key 92a. At the same time keyway 819 of sleeve 78 engages key 92a thereby locking segment A in place through key-collar a. Now, segments, B through F rotate in accordance with the rotation of drive shaft engaging means 28 while segment A remains fixed. It can be seen, therefore, that as the solid portion 82 and sleeve 78 are lowered, each successively lower segment is locked in place while the remaining segments remain free to rotate.

Returning to FIGURE 1, when drive shaft engaging means 28 becomes engaged with a desired segment, as previously described, it is locked into position by engaging the spring loaded pin 94- With the proper groove 96 of slotted section 72. Pin 94 is held by housing 98. In order that the operator may know that the proper tray has been engaged, tray numbers 100 may be noted on a metallic strip 102. Strip 102 will move up and down in accordance with the up and down movement of the drive shaft, in a manner to be described subsequently, until the proper number is indicated in a window of drive shaft cover 104. Drive shaft engaging means 28is free to move up and down into space 42a within hollow drive shaft 26 so as to be capable of engaging any desired segment actuating means, as Well as turn within neck tube 4-2.

The indexing operation of the invention will be described with reference to FIGURE 3. Referring now to FIGURE 3, ingress and egress to the storage space within inner vessel is gained'by removing a pie-shaped plug 105 of removable cover means 18; The diameter of' removable cover means 18 is substantially the same as-that of the inner vessel 10 thereby allowing the plurality of rotatable trays and their drive shaft segments to be removed. As has been previously described, this permits the number and spacing of the trays to be easily varied. It also permits the trays and hollow drive shaft 24 to be removed in case of damage without damaging the container. Thus, the loss of an expensive doublewalled, vacuum-insulated container is prevented should failure of the storage apparatus occur.

Hollow drive shaft 24 is segmented according to the trays so that the trays may be independently rotated, each tray being mechanically connected to hollow drive shaft 24. By raising or lowering a handwheel 106, connected to the top of drive shaft engaging means 28, such means will engage a collar of a segment carrying the tray to be rotated as previously described. Once the desired segment has been engaged, drive shaft engaging means 28 is locked in place by spring loaded pin' 94. Each tray is divided into a plurality of semi-circular sections 108, radial support members 109, one section being open for access to the lower trays. This open sector will also be aligned with the space left by the removal of the plug 105. In the particular embodiment shown, there would be six of such sectors. After engagement of the proper segment of hollow drive shaft 24 with drive shaft engaging means 28 for a particular tray, rotation of the handwheel 106 selects the desired sector. It should here be noted that all of the trays above the one to be'rotated will remain stationary, and since the trays beneath it will also be mechanically connected to the drive shaft (as has been described) they too will rotate. Thus, the open sector 110 of the trays above the tray being rotated will remain in vertical alignment for ingress and egress to the tray. Likewise the trays beneath it will also remain vertically aligned with respect to each other. Tray and sector indicators 112 and 114 are mounted on drive shaft engaging means 28 so that as such means is raised or lowered and rotated, numbers corresponding to the trays and the sectors will appear in the windows of the indicators on drive shaft'cover 104.

Plug 195 is preferably thermally insulated by either of the methods employed in cover means 18. That is, it may contain either the powder-opacified insulation or the fiber sheet-radiation shielded insulation.

In the preferred form of the invention each sector, except the open sector, contains a receptacle 116. The receptacles may be compartmented according to the variety of substances and the amount of separation that is desired. Indexing template 113 contains a hole so that when linkage 122 is positioned by pin 124, receptacle retrieval mechanism 12 6'will be vertically aligned with a coupler 128 of the receptacle. Any type of coupler, such as a ball and socket arrangement could be used. Retrieving mechanism 126 consists of a shaft 13% composed of racks or a single rack that are driven up'and down through a gear when crank 132 is turned. Alternately, the shaft could be provided with a hook or a plurality of hooks capable of engaging corresponding loops positioned on the receptacles.

By using pie-shaped receptacles maximum utilization of the storage space within the container can be achieved. These receptacles when used in conjunction with the pieshaped plug of removable cover means 18 permits the receptacles to be easily removed without having an excessively large opening in the container, thus minimizing the heat leak. Also the receptacles will nearly fill the opening when moved up to the opening for access to its contents. There will, therefore, be little danger of accidentally dropping stored biologicals back into the liquid refrigerant.

Alternatively, a plurality of receptacles, each having a separate coupler, could be carried by a tray sector. Template 118 would then have a plurality of holes 120 to align the retrieval mechanism 126 with the particular coupler of a receptacle. This would allow the substances that are not being used to remain within the cold storage area. The single receptacle is, however, preferred from the standpointof ease in removing and inserting the same.

Referring to FIGURE 1, after a desired tray has been located, the trays may be rotated until a desired portion of the tray is indicated by corresponding numbers 132 indicated on drum 134, numbers 132 being visible through a corresponding window (114 of FIG. 3) in the drive shaft cover 104. Drum 134 rotates in accordance with the drive shaft engaging means 28 through a rod 136 which is connected to a. disk 138 attached to drive shaft engaging means 28. For illustrative purposes as- 'sume on drum 134 indicates the removed or open sector of the trays. When indicated in window 114 of FIG. 3, the removed sector will be aligned with.pieshaped plug 105 of removable cover means 13.

Since each tray above the one desired is locked into place, it is necessary that the removed sectors of these trays (110 of FIG. 3) be in vertical alignment after they are locked in place so that the desired tray can be easily accessible. To accomplish this, it is necessary to return the trays that are being rotated back to the 0 position 'before the next tray is selected. This will insure that the tray sectors will be in vertical alignment.

The operation of theapparatus described thus far can be explained by the following illustration.

For illustrative purposes a typical indexing code might be 4-3, wherein 4 is the tray, and 3 is the tray sector.

Using this code and referring to PEG. 3, the operation would be:

(1) Tray indexing (a) Rotate handwheel ltl until number 0 appears in in sector window 114.

(b) Pull tray index locking pin 94.

(c) Raise or lower handwheel until number f4" in tray window 112.

(d) Release locking pin 94.

(2) Sector indexing appears (a) Rotate handwheel 106 until number 3 appears in sector window 11 The handwheel may be rotated in either a clockwise or counterclockwise direction.

(3) Receptacle removal (a) Remove plug 105. (12) Set pin 124 in hole 120 of indexing template 118. (c) Remove receptacle with retrieval mechanism 126.

(4) Receptacle removal using the alternative form of the invention-that is, each tray sector containing a plurality of receptacles. Indexing code would now be 43-2, wherein 2 is the receptacle in the sector.

7 Numbered drum 134 is rotatably driven by rod 136, drum 134 being free to rotate around tubular section 76. Drive shaft cover 104- is attached to housing 93 through a plurality of bolts 142, the housing in turn being preferably welded to the removable cover means 18 through upper support disk 44.

Leakage of moist atmospheric air down through the drive shaft is prevented by O-ring seal 144. Such leakage of moist air would cause severe operating ditficulties because of the ice formed when the air mixes with the vapors of the low boiling liquid refrigerant. The O-ring seal is held in place by the nut 145 which is threaded to ring 148 which is preferably welded to ring 159, which in turn is preferably welded to the housing 98. The O- ring seal is preferably fabricated from Teflon for minimum friction against drive shaft engaging means 28.

In somecases, depending upon the use of the storage container, it may be desirable to use receptacles that are taller than the space provided between the rotating trays. In such cases additional storage space can be provided by individually removing the trays and substituting one of the segments A through F with a segment having no tray attached. To remove the trays, the drive shaft engaging means 28, cover means 18, collar 68, and coupling 66 are simultaneously removed. The individual trays can then be removed.

In the low temperature storing of such perishable substances as biologicals, it is often necessary to have part of the biologicals immersed within the liquid refrigerant with the remainder being stored above the liquid refrigerant level in the vapor phase of the container. Such biologicals requiring immersion could be stored in receptacles placed on the lower trays of the refrigerator of the invention while those requiring storage in the vapor phase could be Stored in receptacles placed on the upper trays. To accomplish this, means are provided in the present invention to maintain the liquid refrigerant at any desired liquid level.

One of the problems that is associated with maintaining a constant liquid level is that if a single level is maintained, the cycling of the filling system becomes prohibitive because of its frequency of operation. That is, if a single level is maintained, the filling operation will be quite frequent due to the loss of liquid from evaporation. Since a certain percentage of the liquid refrigerant will be lost in cooling down the fill line leading to the charging container, it is preferred to use a pair of sensing devices so that a tolerable range of liquid levels could be maintained, thus reducing the number of times that the filling system needs to be operated. For example, if the sensing devices were placed vertically from 2 to 3 inches apart in a cryogenic refrigerator having a storage area 31.5 inches in diameter and 30 inches in height the filling cycle would be initiated approximately every 4 to 5 days. Thus, one of the sensing devices would be placed at a minimum level and the other at a maximum desired level.

This is accomplished by the liquid level control of the present invention wherein a pair of thermistors, one at the minimum desired level and the other at the maximum level, are used to actuate a solenoid valve placed in a liquid fill line. A thermistor is Well known in the art as being a material, such as nickel oxide, that has a rapid, non-linear change in electrical resistance with respect to temperature. Usually the thermistor increases in resistance as the temperature decreases. This change in electrical property can be used to trigger electronic control or measuring circuits. The operation of this liquid level controller can be described with reference to FIG. 4.

Referring to FIG. 4, the liquid is supplied to a doublewalled thermally insulated cryogenic refrigerator through a fill line from a storage cylinder. The liquid level is sensed through a pair of thermistors 15 and 17 located within the refrigerator. The thermistors are connected to a control panel which also contains the power supply for the system. The flow of liquid through the fill line is controlled by an off-on solenoid valve 21 which is actuated through the control panel by the thermistors i5 and 17.

The following table illustrates the sequence of operations for the thermistors 15 and 17 and the solenoid valve 21, starting with the liquid at the maximum level.

Minimum Maximum Solenoid Step No. Level Level Valve Therrnistor Therrnistor By examining the table with particular reference to steps 2 and 4, it can be seen that although the thermistors are at the same condition in both steps, the solenoid valve is OFF in the one case and ON in the other. This apparent contradiction in operating conditions has been met by the novel circuitry schematically depicted in control panel 1? of FIG. 4. The circuit essentially consists of the two thermistors 15 (max.) and 17 (min), a pair of relay coils 2 3 and 2% which serve to operate the normally open single pole switch 31 and the normally open double pole switch 33, respectively, and the solenoid valve 21. Resistor 35 is not an essential part of the circuit. It does, however, tend to balance out resistance fluctuations in portions of the circuit and thus produce desired operating current through coil 29.

The circuit is basically divided into three parts: (1) The circuit composed of line 37 connected to a power supply terminal, thermistor 17, coil 23, and line 3?, line 39 being connected to ground. (2) A parallel-series circuit, one leg of the parallel poition consisting of line 41 connected to a power supply, resistor 35, switch 31, and line 45, and the other leg consisting of line 47, one pole of switch 33, line 49, and thermistor 15. This parallel circuit is then connected in series with line 45 and coil 29 which is then connected to ground. (3) The circuit composed of line 51 connected to a power supply, the other pole of switch 33, line 53, and solenoid valve '21 connectedto ground. The red pilot light 55, which indicates whether the solenoid valve 21 connected is open, is connected in parallel with the valve. The toggle switch 57 and the yellow light 59 are not essential features of this circuit. Their connection could easily be made by one skilled in the art. For example, they could be positioned in power supply lines 61 and 63.

The operation of the circuit can best be described by following the steps in the above table:

Step 1.With the liquid level at the maximum, both thermistors are cold with substantially no current flowing through the circuit.

Step 2.-As the liquid level drops, thermistor 15 will become warm. Although the thermistor will be warming up, there still will be substantially no current flowing since neither the legs of the parallel circuit will be closed through either of the switches 31 and 33. That is, the thermistor cannot energize the switches itself.

Step 3.Both thermistors become warm as the liquid level drops below the minimum. Now current will flow in the first circuit to energize coil 23 which will close switch 31. This causes current to flow in the parallelseriescircuit, thereby energizing coil 29 to close double pole switch 33'. Current will now flow in the third circuit to energize the solenoid valve 21. Red pilot light 55'will also be energized.

Step*4.-Thermistor 17 becomes cold as liquid is supplied. Coil 23 will no longer be energized and, hence, switch 31 will be open, thus stopping the flow of current in the one leg of the parallel circuit. There will, however, be curr nt in the other leg by virtue of the fact that switch 33 will remain closed so long as there is current passing through thermistor 15. Therefore, the solenoid valve will remain open.

Step 5 .Upon the liquid reaching the maximum level, both thermistors become cold with a minimum of current flowing in both. Coil 29 will now no longer be energized, thus double pole switch 33 will be open. Therefore, there will no longer be current in lines 51 and 53 and solenoid valve 21. This closes the valve.

Thus, it can be seen that with this novel circuitry the maximum level thermistor acts only to keep the solenoid valve 21 open until the maximum level is reached, while the minimum thermistor 17 opens the valve to start the flow of liquid. This novel circuitry, therefore, permits the liquid to be maintained between a maximum and a minimum level, both of which may be easily varied as desired by merely adjusting the depth to which the particular thermistors are inserted in the storage container.

To place the automatic level control system in operation, a toggle switch 57 mounted on the control panel is placed in the ON position. Yellow pilot light 59 indicates when the control system is in service. As the liquid in the container drops to a pre-set minimum limit 15, the solenoid operated valve 21 is opened and liquid will flow to the container, thereby raising the level to the preset maximum limit 17. At this point, the valve is closed.

10 Red pilot light 55 indicates when the valve is open. This, however, does not necessarily mean that liquid is in fact flowing. The flow of liquid can generally be determined by the frosting of the fill line 11. Alternatively, if the red pilot line remains lit for an appreciable length of time,

then it could be presumed that there is no liquid flowing.

Clearly, this liquid level control circuit can be applied to almost any system where a refrigerant liquid level must be maintained within upper and lower limits.

Although preferred embodiments of the invention have been described in detail, it is contemplated that modifications of the apparatus may be made and that some features may be employed without others, all within the spirit and scope of the invention.

What is claimed is:

1. In a thermally insulated liquefied-gas refrigerator having an opening in the upper end for access therein, thermally insulated cover means positioned in said opening, means for storing and indexing within the refrigerator a plurality of storage receptacles which comprises a hollow, segmented, vertically aligned, rotatably mounted, central drive shaft so constructed that each of such segments are rotatable independently of the others and at least one such segment has a rotatable receptacle tray connected thereto; rotatable drive shaft segment actuating means located within the hollow drive shaft and connected to said hollow drive shaft for independent rotation of said segments; rotatably mounted drive shaft engaging means vertically aligned within said hollow drive shaft and extending through said cover means for engaging said rotatable drive shaft segment actuating means within said'hollow drive shaft and rotating said segments from the exterior of the refrigerator.

2. Storing and indexing means according to claim 1 wherein said drive shaft segment actuating means comprises individual key-collars each connected to a respective hollow drive shaft segment and located in vertical adjacency at the upper end of said hollow drive shaft such that each key-collar is rotatable independently of the others; and said drive shaft segment engaging means comprises keyway means for engaging said key-collars.

3. Storing and indexing means according to claim 2 wherein said drive shaft segment engaging means comprises means for selecting and rotatably positioning a desired segment such that all segments below said desired segment will be identically rotatably positioned in vertical alignment therewith and all segments above said desired segment will be maintained in a predetermined stationary position.

4. Storing and indexing means according to claim 2 wherein said drive shaft segment engaging means com prises means for selecting and rotatably positioning a desired segment such that all segments below said desired segment will be identically rotatably positioned in vertical alignment therewith and all segments above said desired segment will be maintained in a predetermined stationary position; and wherein the receptacle trays connected to said drive shaft segments are divided into pie-shaped sections and each such receptacle tray has a pie-shaped opening therein providing for access to the next lower receptacle tray; and said thermally insulated cover means has a removable pie-shaped section positioned for access to the desired receptacle tray through said thermally insulated cover means when such pie-shaped section is removed.

5. A double-walled, vacuum-insulated, liquefied gas cryogenic refrigerator comprising in combination, an inner vessel having an opening in the upper end thereof; an outer shell substantially surrounding said inner vessel and having an opening in the upper end thereof; means for vacuum-tightly sealing the upper end of said outer shell to the upper end of said inner vessel thereby forming an access opening in the cryogenic refrigerator and defining with said outer shell and said inner vessel an evacuable insulation space between said outer shell and said inner vessel; a removable double-walled, vacuum-insulated cover means for substantially closing said access opening;

means for storing and indexing within said inner vessel a plurality of storage receptacles which comprises a hollow, segmented, vertically aligned, rotatably mounted, central drive shaft wherein each of'such segments are rotatable independently of the others and at least one such segment has a rotatable receptacle tray connected thereto;

rotatable drive shaft segment actuating means located within the hollow drive shaft for independent rotation of said segments; rotatably mounted drive shaft engaging means vertically aligned within said hollow drive shaft and extending through such cover means for engaging said rotatable drive shaft segment actuating means within saidhollow drive shaft and rotating said segments from the exterior of the refrigerator.

6. A cryogenic refrigerator according to claim wherein said evacuable insulation space and the cover means are substantially filled with opacificd insulation.

7. A cryogenic refrigerator according to claim 5 wherein said drive shaft segment actuating means comprises individual key-collars each connected to a respec tive hollow drive shaft segment and located in vertical adjacency at the upper "end of said hollow drive shaft such that each such key-collar is rotatable independently of the others; and said drive shaft segment engaging means comprises keyway means for engaging said key-collars such that by turning said shaft segment engaging means and thereby turning the engaged key-collars, said segnients connected to said key-collar will rotate.

trays connected thereto above said desired segment will be maintained in a predetermined stationary position.

9. A cryogenic refrigerator according to claim 8 wherein the receptacle trays connected to said segments are divided into pie-shaped sections and each such receptacle tray has a pie-shaped opening therein providing for access to the next lower receptacle tray such that upon selecting and rotatably positioning a desired segment, including all segments having receptacle trays connected thereto thereunder, access may be gained through the pie- Y shaped openings of the receptacle trays connected to the stationary segments .thereabove; and said thermally insulated cover means has a removable pie-shaped section so positioned that access to the desired receptacle tray may be gained through said thermally insulated cover means when such pie-shaped section is removed.

in resistance of such thermistors in accordance with the liquid level.

12. A cryogenic refrigerator according to claim 11 wherein said control circuit comprises a lower liquid level electrical circuit comprising said lower liquid level thermistor and a coil of a single-switch relay connected to an electrical power supply in series relationship therewith; a parallel-series upper liquid level electrical circuit wherein a first leg of the parallel portion of such circuit comprises said upper liquid level thermistor in series relationship with a first switch of a double switch relay and a second leg of such parallel circuit includes the switch of said single switch relay and an electrical power supply, both legs of such parallel circuit being in series relationship with the coil of said double switch relay; a liquefied gas filling circuit comprising a liquefied gas solenoid control valve, a second switch of said double switch relay and an electrical power supply in series relationship therewith.

13. In a cryogenic refrigerator according to claim 1 having at least one vertically mounted rotatable receptacle tray positioned therein, the combination with the otatable tray of a receptacle retrieval mechanism comprising, in combination, a shaft having means at its lower end for engaging receptacles positioned on the rotatable tray; and means for raising and lowering said shaft into the refrigerator through an offset opening in the upper end thereof whereby receptacles may be inserted and removed from said refrigerator.

References Cited in the file of this patent UNITED STATES PATENTS 2,559,121 Hertzberg July 3, 1951 2,695,729 Hornish Nov. 30, 1954 2,746,480 Hildyard May 22, 1956 2,756,765 Agnle et al July 31, 1956 2,779,652 Orr Jan. 29, 1957 2,856,255 Doesken Oct. 14, 1958 2,984,994 Hankins May 23, 1961 3,075,670 Brugger Jan. 29, 1963 

1. IN A THERMALLY INSULATED LIQUEFIED-GAS REFRIGERATOR HAVING AN OPENING IN THE UPPER END FOR ACCESS THEREIN, THERMALLY INSULATED COVER MEANS POSITIONED IN SAID OPENING, MEANS FOR STORING AND INDEXING WITHIN THE REFRIGERATOR A PLURALITY OF STORAGE RECEPTACLES WHICH COMMPRISES A HOLLOW, SEGMENTED, VERTICALLY ALIGNED, ROTATABLY MOUNTED, CENTRAL DRIVE SHAFT SO CONSTRUCTED THAT EACH OF SUCH SEGMENTS ARE ROTATABLE INDEPENDENTLY OF THE OTHERS AND AT LEAST ONE SUCH SEGMENT HAS A ROTATABLE RECEPTACLE TRAY CONNECTED THERETO; ROTATABLE DRIVE SHAFT SEGMENT ACTUATING MEANS LOCATED WITHIN THE HOLLOW DRIVE SHAFT AND CONNECTED TO SAID HOLLOW DRIVE SHAFT FOR INDEPENDENT RO- 